Above: Knee X-ray (image © istockphoto.com/Bunyos)

When you hold a pencil or type on a keyboard, your joints make the movement of your finger bones possible. Joints are the points where your bones connect, and almost all of your joints contain a flexible yet strong material called cartilage.

Without cartilage, your bones would gradually be worn down by friction. As you can imagine, that would be very painful. So people with damaged joints will be happy to learn that substances called hydrogels are making it possible to repair cartilage faster, more reliably, and with stronger results.

Did you know? One hydrogel currently in development is primarily made of polyvinyl alcohol (used in contact lens solutions and eye drops) and chitosan (derived from shrimp and crab shells).

Articular cartilage is the cartilage that covers the ends of your bones. Disease or injury can cause serious articular cartilage damage. In these cases, a surgical procedure called microfracture is used to stimulate articular cartilage regrowth.

Microfracture involves punching tiny holes in your bones near the damaged cartilage, so that the stem cells in your bone marrow can be released. Stem cells are cells that can differentiate, or grow into any number of different types of cells. Microfracture releases stem cells in the hope they will grow into cartilage cells. Unfortunately, the process is painful, there is no guarantee of cartilage growth, and re-grown cartilage may not be as strong as the original.

However, articular cartilage damage can be repaired more quickly and effectively using hydrogels. As the name suggests, hydrogels are gel-like polymers that are hydrophilic, or “water-loving”. This is an important property, considering that the human body is made mostly of water!

Polymers, which are essentially long chains of repeating molecules called monomers, are like a beaded necklace: the individual beads are the monomers, and the necklace is the polymer. With the right monomers, a polymer will be strong and flexible. The way a polymer interacts with other polymers also affects its physical properties. But the key idea here is that the hydrogels are a type of polymer engineered to be water-loving, strong, and flexible.

Did you know? Hydrogels are being developed to deliver drugs to specific locations in the body. Once the drug arrives at the target site, the hydrogel naturally breaks down.

So how exactly does this relate to damaged joints? It’s a bit like adding fertilizer to your garden: the flowers would likely grow anyway but they require a “special something” to look really bright and healthy. For cartilage regrowth, this “special something” is the hydrogel. It provides a base or scaffold for cartilage regrowth. Studies have shown that injecting hydrogels into the cartilage, in conjunction with microfracture, allows stem cells to grow faster and create stronger cartilage.

Currently, hydrogels need to be “glued on” using a separate adhesive. But new hydrogels that are currently in development can act as both a scaffold and an adhesive.

The medical uses of hydrogels are not limited to repairing articular cartilage. For example, hydrogels have also been used as a scaffold for building blood vessels. Once the blood vessels have grown, the hydrogel breaks down naturally inside the body, in much the same way that some stitches dissolve on their own.

Whether it is growing cartilage or blood vessels, hydrogel technology shows remarkable promise in the medical field. The possibilities are practically endless. One day, with a bit of help from these watery gel-like substances, it might become possible to regrow badly damaged skin, muscles, and possibly even organs!

References:

Science news websites

Biomedical Uses for Hydrogels Explored (Science Daily) Tissue Engineers Report Knee Cartilage Repair Success With New Biomaterial (Science Daily) Step Closer to Custom-Building New Blood Vessels (Science Daily) Repairing Articular Cartilage Defects With an Injectable Gel Engineered with Gene Modified BMSCs (Science Daily)

Scholarly publications

Sharma B, et al. 2013. Human Cartilage Repair with a Photoreactive Adhesive-Hydrogel Composite. Science Translational Medicine. 5(167):167ra6. Lum L, Elisseeff J. 2003. Injectable hydrogels for cartilage tissue engineering. Topics in Tissue Engineering. 16(1):343-353. Jin R, et al. 2009. Injectable chitosan-based hydrogels for cartilage tissue engineering. Biomaterials. 30(13):2544-2551.

Amanda Edward

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